Black grass bugs
Order: Hemiptera
Family: Miridae
Description
Black grass bugs are an assemblage of insect species from two genera, Irbisia spp. and Lapobs spp. They are small, black true bugs that are native to the western rangeland and can cause considerable damage to certain range grasses. These insects have been reported in Arizona, Colorado, South Dakota, North Dakota, Idaho, Montana, Nebraska, Oregon, New Mexico, Utah, Washington, and Wyoming. Several species of black grass bugs can be found in Colorado, with the most common being Labops hesperius. A second species, Irbisia brachycera may be locally abundant as well. Adult black grass bugs are 6.5 mm (¼ inch) in length. Adults of I. brachycera are mostly black, while adults of L. hesperius have black bodies with white margins on the wings and abdomen. It should be noted that Labops spp. are very similar morphologically. Immature stages of black grass bugs are similar in appearance to adults, but smaller. One generation of black grass bugs is produced annually.
Quick Facts
- Black grass bugs are small, black true bugs that are native to the western rangeland and can cause considerable damage to certain range grasses.
- Injury is most pronounced on the upper surface of the leaf and may look straw-colored, similar to frost damage.
- Injury may make grass unpalatable to cattle or prevent seed formation.
Black grass bug. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org.
Image credit: Frank Peairs, Colorado State University, Bugwood.org
Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
Black grass bugs overwinter as eggs that hatch the following spring. Peak feeding tends to occur in late spring and early summer since the emergence of nymphs is associated with the greening of early season wheatgrass (Agropyron spp.), although delayed hatch is observed during colder springs. Early season nymphs tend to reside in grass detritus and soil cracks and develop through five instars. Development is complete in about one month, depending on environmental conditions, most notably temperature and photoperiod. Females lay eggs in the center of dried stems. An adult female can lay around 20 eggs over a one-month lifespan.
Black grass bugs are most active during the evening hours. These insects live in close association with their host grasses, with monocultures of crested wheatgrasses supporting large and destructive populations of black grass bugs. These insects have been observed leaving grass stands that are heavily consumed by cattle. In Colorado, black grass bugs have been documented expanding from sub acre plots of crested wheatgrass to thousands of acres in as little as a few years. Black grass bugs produce one generation each year.
Injury
Black grass bugs have a wide range of hosts. These insects prefer feeding on grasses and have a strong preference for crested wheatgrass. Most injury to crops occurs in the spring with their piercing/sucking feeding, which results in the destruction of chlorophyll and reduces grass vigor and palatability to cattle. White spots appear on the leaf surface at the site of feeding soon after. Injury is most pronounced on the upper surface of the leaf and may look straw-colored, like frost damage. Heavy infestations may prevent seed formation, and when combined with drought conditions or grazing, repeated infestations can kill host plants. Feeding injuries can also be observed in crops adjacent to rangelands.
Monitoring
Scouting for black grass bugs should be conducted in the spring as temperatures warm and the eggs begin to hatch. The use of sweep nets is a common scouting method, although action thresholds for black grass bugs have not been established.
Cultural control
Mowing and removal of hay may be a management technique for reducing the number of eggs in some circumstances. Similarly, grazing management that results in uniformly short vegetation, as opposed to mosaic grazing or resting of the pasture, can significantly reduce the impact of black grass bugs in crested wheatgrass. However, this approach may destroy new plantings of crested wheatgrass and can also reduce the availability of habitat for natural enemies, such as assassin bugs (Hemiptera: Reduviidae).
Chemical control
Due to environmental considerations and costs, insecticides are not typically recommended for managing black grass bugs. Insecticides will kill the adult insects but will have no effect on eggs laid in grass stems. If enough eggs are present, a reinfestation may occur in the next growing season. One well timed application of insecticide may reduce bug numbers to a non-economic level for many years.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
Kneeland, A. 2010. Detection and integrated pest management for black grass bugs. A Thesis: University of Wyoming. Available https://colostate.primo.exlibrisgroup.com/discovery/fulldisplay?docid=cdi_proquest_journals_807621184&context=PC&vid=01COLSU_INST:01COLSU&lang=en&search_scope=MyCampus_FC_CI_PU_P&adaptor=Primo%20Central&tab=Everything&query=any,contains,black%20grass%20bug%20management&offset=0
O’Neill, K., S. Blodgett, B. Olson, and R. Miller. 2008. Impact of livestock grazing on abundance of miridae and reduviidae (Hemiptera) in crested wheatgrass pastures. Journal of Economic Entomology. 101(2): 309-313. Available https://colostate.primo.exlibrisgroup.com/discovery/search?search_scope=MyCampus_FC_CI_PU_P&primoQueryTemp=Impact%20of%20Livestock%20Grazing%20on%20Abundance%20of%20Miridae%20and%20Reduviidae%20(Hemiptera)%20in%20Crested%20Wheatgrass%20Pastures&vid=01COLSU_INST:01COLSU&search_field=any&query=any,contains,Impact%20of%20Livestock%20Grazing%20on%20Abundance%20of%20Miridae%20and%20Reduviidae%20(Hemiptera)%20in%20Crested%20Wheatgrass%20Pastures&lang=en&tab=Everything